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Abstract During the copepodid phase of copepod development, one new somite is added to the body at each moult, and this new somite is anterior and adjacent to the anal somite in which it was formed during the previous stage. A limb on this somite initially will appear as a bud on the following stage, and the bud will be reorganized into an adult-like limb on the next stage. If these attributes are extrapolated from the first copepodid with a body of twelve somites, then the last nauplius has a body of eleven somites: viz., an anterior cephalic somite (corresponding to the protocerebrum), and second and third cephalic somites bearing antenna 1 and antenna 2 (deutocerebrum and tritocerebrum), fourth to sixth cephalic somites bearing mandible, maxilla 1, and maxilla 2; first to third thoracic somites that are bearing buds of maxilliped and buds of swimming legs 1 and 2, a limbless fourth thoracic somite and an anal somite. If one somite is subtracted for each intervening naupliar moult, the body of the orthonauplius is composed of six somites, viz., protocerebrum, deutocerebrum, tritocerebrum, fourth to sixth cephalic somites, plus the anal somite; this is the first hypothesis for the number of somites of an orthonauplius. Whether changes between the last nauplius and first copepodid represent a metamorphosis remains unresolved. A generalized model of the relationship between somite development and limb structure is herein proposed: a somite forms as a simple cylinder within the anal somite; on the following stage this cylindrical somite separates from the anal somite; on the next stage a limb bud is added to the cylindrical somite; on the following stage this bud is then reorganized into a limb resembling the adult limb. Exceptions to the generalizations above are noted, and a fanciful copepod with seven copepodid stages is formulated.